Electron discharge device



April 26, 1932. A. w. HULL 1,855,335

ELECTRON DI SGHARGE DEV I CE Filed March 5, 1924 Fig.2. Fig.5.

Inventor: Albert W. HUI l,

JOB HIS Attorney.

Patented Apr. 26, 1932 UNITED STATES PATENT OFFICE ALBERT W. HULL, OF SGHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC -COMPANY, A CORPORATION OF NEW YORK I ELECTRON DISCHARGE DEVICE Application filed March 8, 1924. Serial No. 698,665.

' fourth grid electrode interposed between the y control grid and the anode. By proper circuit connections this electrode serves to screen the grid and plate, and thereby eliminate capacity effect between these two electrodes. As a result the degree of amplificago tion obtained with a single device may be greatly increased.

I have found, however, that by proper construction of the electron discharge device an additional advantage may be obtained over that which may be obtained if the extra grid is located and constructed in the usual manner. If the screening grid is made of the same length as the control grid there will still be a remaining capacity effect between the control grid and the anode due to the leakage of electrostatic lines of force around the end of the screening grid. Also if the leads by which current is supplied to the different electrodes are parallel to one another as there will be a sufficient capacity between the leads of the anode and control grid to materially affect the operation of the device.

The object of my present invention is to overcome this disadvantage and provide a construction in which the capacity effect between the control grid and anode is reduced to such a degree that it produces substantially no effect in the operation of the device. This object may be attained in various ways. In some cases I provide a screening grid which is materially longer than the control grid and anode and extends an appreciable distance beyond both ends of the control grid and anode or is otherwise arranged to effectively intercept the electrostatic lines of force which Spread out beyond the ends of the control grid and anode. To avoid the capacity effect between the leads the lead for the control grid is preferably brought out of the evacuated receptacle at the opposite end from the anode lead. In case it is not desirable, however, to have leads brought out from both ends of the receptacle the grid lead may be surrounded by a metallic sheath insulated therefrom and this sheath may be grounded. In this way all the leads may be brought out from one end of the receptacle and the capacity effect between the grid and anode very effectively eliminated. Other expedients which will be more fully described may also be used for accomplishing the same purpose.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 shows an elevation partly broken away of a device constructedin accordance with my invention, with the control grid lead brought out of the receptacle at the opposite end from the anode; Fig. 2 is a modification in which all of the leads are brought out at one end of the receptacle; Fig. 3 shows a slight modification of the device of Fig. 1, and Fig. 4 indicates a modified form of grid construction.

I have indicated in Fig. 1 an evacuated receptacle 1 in which are mounted a V-shaped filamentary cathode 2, a control grid 3, an anode 4, and a screening grid 5, which is interposed between the control grid and the anode. The current for the cathode is supplied through the stem 6 by means of the leading-in conductors 7 and 8. The end of the cathode 2 remote from the stem is supported by means of a spring 9 secured to the end of a supporting rod 10. The opposite end of the supporting rod 10 is embedded in a block 11 of insulating material, this block of insulating material being secured to supports 12 and 13, the opposite ends of which are embedded in the stem 6. The screening grid 5 is secured by the transverse supports 14 to supporting members 12 and 13. The supportin member 12 extends through the stem 6 an forms a continuation of the leading-in conductor 15 by which current is supphed to the screening grid. The supports 16 and 17 of the control grid are also embedded in the block 11 of insulating material and support 17 is extended through the block and connected to the leading-in conductor 18 whereby current is supplied to the control grid. The anode is supported from the stem 6 by means of supports 19 and 20, and support 20 is connected to leading-in conductor 21 which serves to supply current to the anode.

It will be noted that in the construction described all'of the electrodes are coaxial and the screening grid extends an appreciable distance beyond both ends of the control grid and anode 4, thereby serving to intercept electrostatic'lines of force extending beyond the ends of these electrodes. Thecontrol grid lead is also brought out of the receptacle at the opposite end from the anode lead so that there is no unscreened capacity between the two leads. This construction permits the use of the usual four-electrode base 22 at one end of the device with any simple form of terminal at the opposite end for the control grid lead.

In the form of my invention shown in Fig. 2 all of the electrodes are supported from the stem 6, the screening grid in this case being connected to the leading-in conductor 23. which extends through the stem 6. The lead 24 for the control grid is sealed into theend of a tubular metallic sheath 25 and insulated therefrom. One of the cathode supports 26 is conductively secured to the metallic follow sheath 25. and the metallic sheath 25 is in turn sealed into the stem 6, thereby serving to supply current to the cathode from the leading-in conductor 7, which is conductively secured to the sheath 25 at a point 32. Since one of the cathode terminals is ordinarily grounded, the sheath 25 is at ground potential or at a fixed potential with respect to ground and therefore serves as a screen between the grid lead 24 and the anode lead 21.

The construction shown in Fig. 3 is similar to that shown in Fig. 1. In Fig. 3. however, the inner wall of the receptacle 1 is'covered with a metallic coating 27 and this metallic coating is connected to conductor 28 which in turn issecured to the support 12 of the screening grid. The metallic coating, if desired, may cover the entire interior of recep-- tacle 1. This coating serves to intercept electrostatic lines of force from the anode, which might pass around the endof the screening grid to the control grid and to the lead of the control grid, and thus serves as an additional elementfor screening the control grid from the anode. This form of my invention is claimed in my application Serial No. 301,336, filed August 22, 1928, as a division of the resent application.

In Fig. 4 l have indicated a modified form of'screening id construction in which the screening gri is made up of annular discs 29 threaded on supporting rods 30. A grid made in this way is particularly effective in so far as its screening action is concerned and does not interfere with the flow of electrons to the anode to any greater extent than a grid made of wires of similar thickness. I have indicated at the upper end of the screening grid in this case a disc 31 which is of a diameter nearly equal the internal diameter of the receptacle 1, and such discs may be provided at both ends of the screening grid if desired. This arrangement is also particularly effective in intercepting the lines of force extending from the anode. It will be understood that the supports 14 shown in- Fig. 1 and Fig. 3 may if desired take the form of a disc such as that shown in Fig. 4. This form of screening grid is claimed and the manner in which it may be employed in a device of the form shown in Fig. 1 is more fully illustrated in my application Serial No. 214,198, filed August 19, 1927, as a continuation in part of the resent application.

By the means WhlGh I have described any capacity effect between anode and control grid may be so efi'ectively eliminated as to be entirely inappreciable. As previously constructed the screening grids have only been effective in intercepting electrostatic lines extending directly between the anode and control grid. I have however in the various arrangements shown provided means which are effective in intercepting not only the electrostatic lines extending directly between anode and control grid, but also electrostatic lines extending in curved paths between the two electrodes as well as electrostatic lines extending from the anode to the lead for the control grid, or from the anode lead to the lead from the control 'd.

The potential applied tb the screening grid for producing the screening action is preferably a constant potential so chosen that it has no deleterious efi'ect upon the usual operation of the device. In thecase of the sheath 25 in F1g. 2, or in case of a sheath on the wall of the receptacle which may be either inside of the receptacle, as shown in Fig. 3, or on the outside, the potential impressed upon the screening member may be ground potential or a potential very near ground potential. The potential of the screening grid itself is preferably fixed at a value which is more positive with respect to the cathode than the potential of the control grid at any time.

- While I have shown and described the preferred embodiment of my invention, it will be apparent that many modifications may be made in the structural details employed for carrying my invention into effect without departing from the scope thereof, as set forth in theappended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The combination in an electron discharge device of an electron emitting cathode, an anode and acontrol grid, and anelectrostatic screening member interposed between .the anode and control grid and extending for appreciable distances beyond the ends of the anode and control grid, and means for eliminating the effect of capacity between the leads by which current is supplied to the effect of substantially all capacity coupling between the leading-in conductors which .supply current to the anode and control grid.

3. The combination in an electron discharge device of a receptacle containing an electron emitting cathode, ananode', a control grid and an electrostatic screening member interposed between the anode and control grid and the screening member extending for appreciable distances from the ends of the anode and control grid, a stem through which leading-in conductors for supplying current to all of said electrodes are sealed and means for eliminating the effect of substantially allcapacity coupling between the leading-in conductors which supply current to the anode and control grid. A

4. The combination in an electron discharge device of a receptacle containingan electron emitting cathode, an anode, a control grid and an electrostatic screening member interposed between the anode and control grid, a stem through which leading-in conductors for supplying current to all of said electrodes are sealed, a shield extending through the stem and surrounding the lead conductors for supplying current to said electrodes and conductive shielding means within the device of sufficient extent to intercept substantially all electrostatic lines of force extending from the anode toward the leading-in conductor for the grid.

7. The combination in an electron discharge device of an electron emitting cathode, an anode and a control grid, leading-in conductors for said electrodes, and conductive shielding means within the device of suflicient extent to intercept substantially all electrostatic lines of force extending from the leading-in conductor for the anode toward the leading-in conductor for the grid.

8. The combination in an electron discharge device of an electron emitting cathode, an anode and a control grid and conductive screening means inter osed between the anode and control grid an extending an appreciable distance outside of the space directly between the two whereby the application of asuitable potential to the screening grid will eliminate substantially all coupling between input and output circuits connected to the device due to capacity between the control grid and the anode, and means for eliminating the effect of capacity between the leads by which current is supplied to the anode and control grid.

9. The combination in an electron discharge device, of an electron emitting cath- In witness whereof, I have hereunto set my hand this 29th da of February, 1924.

A BERT W. HULL.

for supplying current to the control grid,

said shield being adapted to have impressed .thereon a fixed potential.

5. The combination in an electron discharge device ,of an electron emitting oath ode, an anode, a control grid, leading-in conductors for supplying current to said electrodes, and conductive shielding means within the device of sufiicient extent to intercept substantially all electrostatic lines of :Eorce extending from the anode and its leading-in conductor toward the conductor. I

6. The combination in an electron discharge device of an electron emittin oath-- 6 ode, an anode and a control grid, leafiing grid and its leading-in 

